Base station, terminal, transmission method, and reception method

ABSTRACT

Disclosed is a base station capable of appropriately configuring a resource on which EPDCCH is located when soft combining is applied. The base station includes configuration section ( 102 ) that configures an EPDCCH set in a plurality of subframes, the EPDCCH set being formed of ECCEs to which control information (assignment information) transmitted over the plurality of subframes is assigned; and an assignment section ( 105 ) that assigns the control information to any of the ECCEs in each of the plurality of subframes.

TECHNICAL FIELD

The claimed invention relates to a base station, a terminal, atransmission method, and a reception method.

BACKGROUND ART

In recent years, it has become common to transmit not only speech databut also a large amount of data such as still image data and movingimage data along with the adoption of multimedia information in cellularmobile communication systems. In addition, studies have been activelycarried out to achieve a high transmission rate using a wide radio band,Multiple-Input Multiple-Output (MIMO) transmission technology, andinterference control technique in Long Term Evolution Advanced(LTE-Advanced).

In LTE-Advanced, an enhanced control channel region called EnhancedPDCCH (EPDCCH), which is an enhanced version of Physical DownlinkControl CHannel (PDCCH) used for control signals, has been designed.EPDCCH is located in a resource region to which downlink data isassigned (i.e., Physical Downlink Shared Channel (PDSCH) region). Basestations can configure each terminal (sometimes called “User Equipment(UE)”) with a frequency resource (e.g., resource block (RB)) in aresource region in which EPDCCH is located (EPDCCH region) and transmitsignals to the terminal. Thus, it is made possible to achievetransmission power control for control signals transmitted to a terminallocated near a cell edge, or interference control for interferencecaused by a cell of the base station to another cell or interferencecontrol for interference caused by another cell to the cell of the basestation due to the control signals to be transmitted.

Each RB has 12 subcarriers in the frequency domain and a width of 0.5msec in the time domain. The unit of two RBs combined in the time domainis called an RB pair. More specifically, each RB pair has 12 subcarriersin the frequency domain and a width of 1 msec in the time domain.Moreover, when an RB pair represents a block of 12 subcarriers on thefrequency axis, the RB pair may be simply called an RB. An RB pair isalso called a Physical RB pair (PRB pair) on the physical layer. Inaddition, the unit defined by one subcarrier and one OFDM symbol is aresource element (RE).

In an EPDCCH region, the units defined by dividing each PRB pair into 16resources are called Enhanced Resource Element Groups (EREGs), and aresource unit formed of four or eight EREGs is called an EnhancedControl Channel Element (ECCE). The number of ECCEs forming EPDCCHtransmitting one set of control signals is called an aggregation level(AL). A plurality of ALs can be configured for EPDCCH (see, Non-PatentLiterature (hereinafter, referred to as “NPL”) 1). In addition, an“EPDCCH candidate” is previously defined in each AL. The term, “EPDCCHcandidate” as used herein refers to a candidate for a region to whichcontrol signals are mapped, and a plurality of EPDCCH candidates form asearch space, which is a blind-decoding (monitoring) target of aterminal.

LTE-Advanced allows each terminal to be configured with a plurality ofEPDCCH sets each formed of a set of ECCEs on which EPDCCH may be located(i.e., control information assignment candidate). Since the positionsand number N of PRB pairs to be used are configured for each EPDCCH set,control signals are arranged more flexibly.

FIG. 1 illustrates an example of how EPDCCHs are mapped to resources.The ECCEs on which EPDCCHs are located are selected from theabovementioned plurality of EPDCCH candidates. In FIG. 1, EPDCCH #0 andEPDCCH #1 are each configured with aggregation level 1 (AL1) whileEPDCCH #2 and EPDCCH #3 are configured with aggregation level 2 (AL2)and aggregation level 4 (AL4), respectively. In FIG. 1, EPDCCH #0 islocated on ECCE #0, and EPDCCH #1 is located on ECCE #1, while EPDCCH #2is located on ECCE #2 and ECCE #3, and EPDCCH #3 is located on ECCE #4,ECCE #5, ECCE #6, and ECCE #7. In addition, since each ECCE is locatedon four EREGs, the ECCE is divided into four pieces in FIG. 1. Asillustrated in FIG. 1, in case of localized assignment, four EREGs arelocated on the same PRB pair, while four EREGs are located on differentPRB pairs in case of distributed assignment.

Incidentally, as an EPDCCH assignment method, there are “localizedassignment” in which EPDCCH is assigned locally to positions close toeach other on the frequency band, and “distributed assignment” in whichEPDCCH is assigned distributedly on the frequency band. “Localizedassignment” is an assignment method used to obtain frequency schedulinggain and enables assignment of EPDCCH to a resource having good channelquality on the basis of channel quality information. “Distributedassignment” allows obtaining frequency diversity gain by distributingEPDCCH on the frequency axis. LTE-Advanced allows both of a search spacefor localized assignment and a search space for distributed assignmentto be configured.

In LTE-Advanced, downlink (DL) assignment indicating DL data assignmentand an uplink (UL) grant indicating UL data assignment are transmittedon PDCCH or EPDCCH. DL assignment reports that a resource in a subframeused to transmit this DL assignment is assigned to a terminal.Meanwhile, UL grant reports that a resource in a target subframepreviously determined by the UL grant is assigned to a terminal.

CITATION LIST Non-Patent Literature

-   NPL 1-   3GPP TS 36.213 V11.1.0, “Physical layer procedures

SUMMARY OF INVENTION Technical Problem

In LTE-Advanced, studies have been carried out to achieve a hightransmission rate at hotspots by installing a small cell, which is abase station using low transmission power. For example, as a carrierfrequency for operating a small cell, a high frequency such as 3.5 GHzhas been considered as a candidate. When a high frequency radio band isused, however, attenuation increases as the transmission distanceincreases, although a higher transmission rate can be expected with ashort distance. Accordingly, there is a problem in that the coveragearea of a small cell decreases when a mobile communication system usinga high frequency radio band is put into operation. In addition, in caseof small cells, the restrictions on transmission power need to be takeninto consideration as well, and the power usable for transmission persubframe is limited. The coverage area of a cell is determined by therange in which control signals can be received. Thus, a technique thatincreases the coverage area of control signals is required.

In this respect, application of soft combining (sometimes called“bundling”) in which EPDCCH including control information is locatedover a plurality of subframes may be possible, for example. However, nostudies have been carried out so far on any EPDCCH location method usedwhen soft combining is applied.

It is an object of the claimed invention to provide a base station, aterminal, a transmission method, and a reception method that are capableof appropriately configuring resources on which EPDCCH is located whensoft combining is applied.

Solution to Problem

A base station according to an aspect of the claimed invention includes:a configuration section that configures an Enhanced Physical DownlinkControl Channel (EPDCCH) set in a plurality of subframes, the EPDCCH setbeing formed of Enhanced Control Channel Elements (ECCEs) to whichcontrol information transmitted over the plurality of subframes isassigned; and an assignment section that assigns the control informationto any of the ECCEs on a Physical Resource Block (PRB) pair in each ofthe plurality of subframes.

A terminal according to an aspect of the claimed invention includes: aconfiguration section that identifies Enhanced Control Channel Elements(ECCEs) to which control information transmitted over a plurality ofsubframes is assigned, the ECCEs forming an Enhanced Physical DownlinkControl Channel (EPDCCH) set configured in the plurality of subframes;and a reception section that receives the control information assignedto any of the ECCEs on a Physical Resource Block (PRB) pair in each ofthe plurality of subframes.

A transmission method according to an aspect of the claimed inventionincludes: configuring an Enhanced Physical Downlink Control Channel(EPDCCH) set in a plurality of subframes, the EPDCCH set being formed ofEnhanced Control Channel Elements (ECCEs) to which control informationtransmitted over the plurality of subframes is assigned; andtransmitting the control information assigned to any of the ECCEs on aPhysical Resource Block (PRB) pair in each of the plurality ofsubframes.

A reception method according to an aspect of the claimed inventionincludes: identifying Enhanced Control Channel Elements (ECCEs) to whichcontrol information transmitted over a plurality of subframes isassigned, the ECCEs forming an Enhanced Physical Downlink ControlChannel (EPDCCH) set configured in the plurality of subframes; andreceiving the control information assigned to any of the ECCEs on aPhysical Resource Block (PRB) pair in each of the plurality ofsubframes.

Advantageous Effects of Invention

According to the claimed invention, it is possible to appropriatelyconfigure resources on which EPDCCH is located when soft combining isapplied.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram provided for describing EPDCCH;

FIG. 2 is a diagram provided for describing soft combining;

FIG. 3 is a block diagram illustrating a main configuration of a basestation according to Embodiment 1 of the claimed invention;

FIG. 4 is a block diagram illustrating a main configuration of aterminal according to Embodiment 1 of the claimed invention;

FIG. 5 is a block diagram illustrating a configuration of the basestation according to Embodiment 1 of the claimed invention;

FIG. 6 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the claimed invention;

FIG. 7 is a diagram illustrating PDSCH and PUCCH timing according toEmbodiment 1 of the claimed invention;

FIG. 8 is a diagram illustrating PUSCH timing according to Embodiment 1of the claimed invention;

FIGS. 9A and 9B are diagrams illustrating switching between soft combingand non soft combining according to Embodiment 1 of the claimedinvention;

FIG. 10 is a diagram illustrating a configuration example of EPDCCHcandidates according to Embodiment 2 of the claimed invention;

FIGS. 11A and 11B are diagrams each illustrating a configuration exampleof EPDCCH search spaces according to Embodiment 2 of the claimedinvention;

FIGS. 12A and 12B are diagrams each illustrating a configuration exampleof EPDCCH search spaces according to Embodiment 2 of the claimedinvention;

FIG. 13 is a diagram illustrating the number of EPDCCH candidatesaccording to Embodiment 2 of the claimed invention;

FIG. 14 is a diagram illustrating a configuration example of EPDCCHcandidates according to Embodiment 3 of the claimed invention;

FIG. 15 is a diagram illustrating PRB pairs (EREGs) on which ECCE islocated according to Embodiment 3 of the claimed invention; and

FIGS. 16A and 16B are diagrams illustrating a configuration example ofthe number of EPDCCH candidates according to other embodiments of theclaimed invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the claimed invention will be described indetail with reference to the accompanying drawings. Throughout theembodiments, the same elements are assigned the same reference numerals,and any duplicate description of the elements is omitted.

Embodiment 1

(Overview of Communication System)

A communication system according to Embodiment 1 includes base station100 and terminal 200. This communication system is an LTE-Advancedsystem, for example. In addition, base station 100 is a base stationcompliant with the LTE-Advanced system, and terminal 200 is a terminalcompliant with the LTE-Advanced system, for example.

In Embodiment 1, when transmitting EPDCCH intended for terminal 200,base station 100 can apply soft combining for transmitting EPDCCH (i.e.,control information) over a plurality of subframes (see, FIG. 2).Receiver side (i.e., terminal 200) performs reception processing aftercombining control information transmitted over a plurality of subframes.The EPDCCH transmitted over a plurality of subframes is formed of a bitsequence that includes an information bit and a redundancy bit and thatis generated by performing error correction coding on the informationbit. In addition, upon reception of the EPDCCH transmitted over aplurality of subframes, terminal 200 determines the timing of datareception or transmission upon completion of EPDCCH reception andACK/NACK (i.e., response signals) transmission or reception.

Higher layer signaling previously configures terminal 200 with subframesto which soft combining of EPDCCH is applied. The configuration of thesubframes may be different for each terminal. In addition, a singleframe may include both of the subframes to which soft combining isapplied and to which no soft combining is applied. This configurationallows switching between soft combining of EPDCCH and non soft combiningdepending on reception quality of each subframe in such a way that softcombing is applied to a subframe subject to a large amount ofinterference while no soft combining is applied to a subframe subject toa small amount of interference.

It should be noted herein that base station 100 and terminal 200 cantransmit and receive control information (i.e., DL assignment or ULgrant) using a PDCCH region or EPDCCH region, but the transmission andreception of control information only in an EPDCCH region will bedescribed hereinafter for simplicity of description.

FIG. 3 is a block diagram illustrating a main configuration of basestation 100 according to Embodiment 1.

In base station 100, configuration section 102 configures an EPDCCH setformed of ECCEs to which control information (assignment information)transmitted over a plurality of subframes is assigned in the pluralityof subframes. Signal assignment section 105 assigns the controlinformation to any of the ECCEs in on a PRB pair in each of theplurality of subframes.

FIG. 4 is a block diagram illustrating a main configuration of terminal200 according to Embodiment 1.

In terminal 200, configuration section 205 identifies the ECCE to whichcontrol information (assignment information) transmitted over aplurality of subframes is assigned and which forms an EPDCCH setconfigured in the plurality of subframes. Control signal receivingsection 206 receives control information assigned to any of the ECCEs ona PRB pair in each of the plurality of subframes.

(Configuration of Base Station 100) FIG. 5 is a block diagramillustrating a configuration of base station 100 according toEmbodiment 1. In FIG. 5, base station 100 includes assignmentinformation generating section 101, configuration section 102, errorcorrection coding section 103, modulation section 104, signal assignmentsection 105, transmission section 106, reception section 107,demodulation section 108, and error correction decoding section 109.

Assignment information generating section 101 determines a resource(i.e., RB) to which data signals are assigned, when downlink datasignals (DL data signals) to be transmitted and uplink data signals (ULdata signals) to be assigned to uplink are present, and generatesassignment information (DL assignment and UL grant). The DL assignmentincludes information on the assignment of DL data signals. The UL grantincludes information on the assignment resource of UL data signalstransmitted from terminal 200. The DL assignment is outputted to signalassignment section 105, and the UL grant is outputted to signalassignment section 105 and reception section 107.

Configuration section 102 configures each terminal 200 with one or moreEPDCCH search spaces. More specifically, configuration section 102configures each terminal 200 with a PRB pair number for locating anEPDCCH search space, an ECCE index for each aggregation level, and thesearch space (EPDCCH) assignment method (i.e., localized assignment ordistributed assignment). An EPDCCH search space is formed of a pluralityof assignment candidates (i.e., EPDCCH candidates). Each “assignmentcandidate” is formed of the same number of ECCEs as the aggregationlevel.

Configuration section 102 assigns an ECCE index for each search spacewhen configuring terminal 200 with a plurality of EPDCCH search spaces.

Configuration section 102 configures terminal 200 to which softcombining is applied, with the subframes to which soft combining isapplied (see, FIG. 2). In addition, configuration section 102 configuresterminal 200 to which soft combining is applied, with an EPDCCH set forthe plurality of subframes to which soft combing is applied. During thisprocessing, the PRB pair corresponding to the ECCEs forming the EPDCCHset is located in each of the plurality of subframes. Accordingly, ineach of the subframes used for soft combining, the search spacedescribed above is configured on the basis of the configured EPDCCH set.

Configuration section 102 outputs information on the configured searchspace and information on the subframe numbers to which soft combining ofEPDCCH is applied to signal assignment section 105. The information onthe search space includes a PRB pair number, the number of PRB pairsand/or the like, for example. In addition, configuration section 102outputs information on the PRB pair configured in the search space, andinformation on the EPDCCH assignment method to error correction codingsection 103 as control information.

Error correction coding section 103 takes transmission data signals(i.e., DL data signals), and the control information received fromconfiguration section 102 as input and performs error correction codingon the input signals and outputs the resultant signals to modulationsection 104.

Modulation section 104 performs modulation processing on the signalsreceived from error correction coding section 103 and outputs themodulated data signals to signal assignment section 105.

Signal assignment section 105 assigns the assignment information (DLassignment and UL grant) received from assignment information generatingsection 101 to any of the ECCEs (ECCE in units of assignment candidates)corresponding to the PRB pair number indicated by the search spaceinformation received from configuration section 102. During thisassignment, when soft combining is configured for the assignmentinformation, signal assignment section 105 assigns the assignmentinformation to any of the ECCEs on a PRB pair in each of a plurality ofsubframes corresponding to the subframe numbers indicated by theinformation on soft combining received from configuration section 102.Accordingly, the assignment information is assigned to the PRB pair onwhich ECCE is located (e.g., see FIG. 1). In addition, signal assignmentsection 105 assigns the data signals received from modulation section104 to a downlink resource corresponding to the assignment information(DL assignment) received from assignment information generating section101.

Transmission signals are thus formed by assignment of the assignmentinformation and data signals to a predetermined resource. Thetransmission signals thus formed are outputted to transmission section106. In addition, signal assignment section 105 notifies receivingsection 107 of the ECCE index of ECCE used for transmission of DLassignment. It should be noted herein that, when soft combining isapplied, signal assignment section 105 notifies receiving section 107 ofthe ECCE index of ECCE in the end subframe (may be referred to as “lastsubframe,” hereinafter) among the plurality of subframes used for thetransmission of DL assignment.

Transmission section 106 performs radio transmission processing such asup-conversion on the received signals and transmits the resultantsignals to terminal 200 via an antenna.

Reception section 107 receives, via an antenna, the signals transmittedfrom terminal 200 and outputs the received signals to demodulationsection 108. More specifically, reception section 107 demultiplexes thereceived signals into signals corresponding to the resource indicated bythe UL grant received from assignment information generating section101, then performs reception processing such as down-conversion on thesignals obtained by demultiplexing and outputs the processed signals todemodulation section 108. Reception section 107 extracts (i.e.,receives) A/N signals from signals corresponding to a PUCCH resourceassociated with the ECCE index received from signal assignment section105.

Demodulation section 108 performs demodulation processing on thereceived signals and outputs the resultant signals to error correctiondecoding section 109.

Error correction decoding section 109 decodes the received signals toobtain the received data signals from terminal 200.

(Configuration of Terminal 200)

FIG. 6 is a block diagram illustrating a configuration of terminal 200according to Embodiment 1. In FIG. 6, terminal 200 includes receptionsection 201, signal demultiplexing section 202, demodulation section203, error correction decoding section 204, configuration section 205,control signal receiving section 206, error correction coding section207, modulation section 208, signal assignment section 209, andtransmission section 210.

Reception section 201 receives, via an antenna, signals transmitted frombase station 100, then performs reception processing such asdown-conversion on the received signals and outputs the processedsignals to signal demultiplexing section 202.

Signal demultiplexing section 202 extracts control signals for resourceassignment from the received signals to be received from receptionsection 201 and outputs the extracted signals to control signalreceiving section 206. In addition, signal demultiplexing section 202extracts, from the received signals, signals corresponding to the dataresource indicated by the DL assignment outputted from control signalreceiving section 206 (i.e., DL data signals) and outputs the extractedsignals to demodulation section 203. When soft combining of EPDCCH isapplied, signal demultiplexing section 202 extracts signalscorresponding to the data resource (DL data signals) from the receivedsignals on the basis of the last subframe among the plurality ofsubframes used for soft combining.

Demodulation section 203 demodulates the signals outputted from signaldemultiplexing section 202 and outputs the demodulated signals to errorcorrection decoding section 204.

Error correction decoding section 204 decodes the demodulated signalsoutputted from demodulation section 203 and outputs the resultantreceived data signals. In particular, error correction decoding section204 outputs the “information on the PRB pair configured in the searchspace” and “information on the subframes to which soft combining ofEPDCCH is applied” to configuration section 205.

Configuration section 205 identifies the search space configured for theterminal using the EPDCCH (i.e., terminal 200). Configuration section205 first identifies the PRB pair to be configured in the search space,on the basis of the information received from error correction decodingsection 204, for example. Configuration section 205 then identifies theEPDCCH to which soft combining is applied, on the basis of theinformation on the subframes to which soft combining of EPDCCH isapplied. Configuration section 205 then determines the ECCE index of thesearch space corresponding to the PRB pair. Accordingly, configurationsection 205 identifies the ECCE to which the EPDCCH to be transmittedover a plurality of subframes is assigned (i.e., ECCE forming the EPDCCHset configured in the plurality of subframes). In this processing, whena plurality of EPDCCH search spaces are configured, configurationsection 205 allocates an ECCE index to each search space. Moreover,configuration section 205 identifies which ECCE index is configured asan EPDCCH candidate for each aggregation level according to rules thatare previously determined for each terminal 200 and is common to basestation 100 and terminal 200. For example, configuration section 205identifies the ECCE index serving as an EPDCCH candidate for eachaggregation level on the basis of the UE ID (i.e., terminal specific ID)and whether or not soft combining is applied. Configuration section 205then outputs the information on the PRB pair and ECCE configured as thesearch space to control signal receiving section 206.

Control signal receiving section 206 performs blind-decoding on the ECCEcorresponding to the PRB pair indicated by the information received fromconfiguration section 205, thereby detecting the control signals (DLassignment or UL grant) intended for terminal 200. More specifically,control signal receiving section 206 receives the control signalsassigned to one of a plurality of assignment candidates forming thesearch space configured by configuration section 205. When softcombining of EPDCCH is applied, control signal receiving section 206receives the control signals assigned to any of ECCHs on a PRB pair in aplurality of subframes. Control signal receiving section 206 outputs thedetected DL assignment intended for terminal 200 to signaldemultiplexing section 202 and outputs the detected UL grant intendedfor terminal 200 to signal assignment section 209. Control signalreceiving section 206 outputs the ECCE index of the ECCE on which the DLassignment is detected to signal assignment section 209.

Error correction coding section 207 takes the transmission data signals(UL data signals) as input and performs error correction coding on thetransmission data signals and outputs the resultant signals tomodulation section 208.

Modulation section 208 modulates the signals received from errorcorrection coding section 207 and outputs the modulated signals tosignal assignment section 209.

Signal assignment section 209 assigns the signals received frommodulation section 208, according to the UL grant received from controlsignal receiving section 206 and outputs the resultant signals totransmission section 210. When soft combining of EPDCCH is applied,signal assignment section 209 determines the transmission subframe forthe signals on the basis of the last subframe among the plurality ofsubframes to which soft combining is applied. In addition, signalassignment section 209 assigns the A/N signals received from errorcorrection decoding section 204 to a predetermined resource. Morespecifically, when transmission data signals are present, signalassignment section 209 multiplexes the A/N signals with the transmissiondata signals and outputs the resultant signals to transmission section210. Meanwhile, when no transmission data signals are present, signalassignment section 209 identifies the PUCCH resource on the basis of theECCE index received from control signal receiving section 206, thenassigns the A/N signals to the identified PUCCH resource and outputs theresultant signals to transmission section 210. During this processing,when soft combining of EPDCCH is applied, signal assignment section 209determines the transmission subframe for the A/N signals on the basis ofthe last subframe among the plurality of subframes to which softcombining is applied.

Transmission section 210 performs transmission processing such asup-conversion on the received signals and transmits the processedsignals.

(Operations of Base Station 100 and Terminal 200)

A description will be provided regarding operations of base station 100and terminal 200 configured in the manner described above.

Hereinafter, a description will be provided for (1) PDSCH timing, (2)uplink A/N signal (UL ACK/NACK) timing, and (3) PUSCH timing when softcombining of EPDCCH is applied.

(PDSCH Timing)

Base station 100 and terminal 200 configure the transmission timing ofPDSCH specified by the DL assignment notified using the EPDCCH to whichsoft combining is applied (i.e., subframe on which the PDSCH is located)to be the last subframe among the plurality of subframes on which EPDCCHto be soft-combined is located.

FIG. 7 illustrates a configuration example of PDSCH timing. Asillustrated in FIG. 7, when soft combining using two subframes, namely,subframes #0 and #1 is applied, base station 100 locates PDSCH forterminal 200 on subframe #1, which is the last subframe among the twosubframes. More specifically, as illustrated in FIG. 7, a resource insubframe #1 is specified as a PDSCH resource in the DL assignmentnotified using the EPDCCH located in subframes #0 and #1.

In other words, base station 100 (i.e., signal assignment section 105)assigns the downlink data (PDSCH) the assignment of which is indicatedby EPDCCH (DL assignment) to the last subframe among the plurality ofsubframes used for soft combining.

Meanwhile, in FIG. 7, terminal 200 (i.e., control signal receivingsection 206) performs blind-decoding on the ECCEs located in subframes#0 and #1 to which soft combining is applied, thereby detecting the DLassignment intended for terminal 200. Terminal 200 (i.e., signaldemultiplexing section 202) extracts PDSCH (DL data signals) in subframe#1 on the basis of the detected DL assignment.

During this processing, detection of DL assignment to be notified usingEPDCCH to which soft combining is applied is performed after receptionof the last subframe in terminal 200. Upon detection of the DLassignment, terminal 200 identifies that PDSCH is assigned to the PRBpair specified by the DL assignment and starts reception processing onthe PDSCH.

For this reason, if PDSCH is located in a subframe ahead of the lastsubframe, terminal 200 needs to store, in a buffer, received signals onall the PRB pairs that may have been assigned to PDSCH until completionof identifying (detecting) the PRB pair assigned to PDSCH.

On the other hand, PDSCH is located in the last subframe among theplurality of subframes to which soft combining is applied inEmbodiment 1. Accordingly, the period for saving, in a buffer, thereceived signals that are received from the reception timing of PDSCH tothe completion of EPDCCH detection can be minimized. To put itdifferently, the period for saving, in a buffer, the received signalsthat are received from the reception timing of PDSCH to the completionof EPDCCH detection when soft combining of EPDCCH is applied can be thesame as the period used when no soft combining of EPDCCH is applied (nonsoft combining). Thus, it is possible to prevent an increase in the sizeof the buffer to be included in terminal 200.

(UL ACK/NACK Timing) In LTE-Advanced, after reception of PDSCH,terminals perform reception determination (i.e., error determination)and transmit uplink A/N signals (UL ACK/NACK) to base station 100 (notillustrated). In addition, the subframe used for transmitting uplink A/Nsignals is previously defined. More specifically, the fourth subframefollowing the subframe to which PDSCH is assigned is configured as thesubframe used for transmitting uplink A/N signals in a frequencydivision duplex (FDD) system. In a time division duplex (TDD) system,the subframe used for transmitting uplink A/N signals is defined foreach TDD UL-DL configuration (i.e., timing configuration in units ofsubframes for downlink communication (DL) and uplink communication (UL)per frame). In both of the FDD system and TDD system, the transmissiontiming of uplink A/N signals is always configured to be the fourth orafter the fourth subframe following the transmission of PDSCH.

In Embodiment 1, the transmission timing of uplink A/N signals (i.e.,subframe used for transmission of UL ACK/NACK) is defined according tothe reception subframe for PDSCH (i.e., subframe in which PDSCH istransmitted). The transmission timing of uplink A/N signals isconfigured to be the fourth subframe following the reception subframefor PDSCH in the FDD system, while the transmission timing of uplink A/Nsignals is defined according to each TDD UL-DL configuration in the TDDsystem, using the subframe on which PDSCH is received, as the basis.Uplink A/N signals are transmitted in a PUSCH region when there is PUSCHtransmission or transmitted in a PUCCH region when there is no PUSCHtransmission.

In LTE-Advanced, when uplink A/N signals are transmitted in a PUCCHregion, a PUCCH resource associated with the smallest ECCE number amongthe ECCEs forming EPDCCH on which DL assignment is located (i.e., EPDCCHsubframe on which PDSCH is transmitted) (i.e., implicitly indicatedresource) is specified so that the PUCCH resource is automatically(implicitly) assigned to avoid a PUCCH resource collision betweenterminals.

Thus, base station 100 and terminal 200 identify the PUCCH resourceassociated with the ECCE number of EPDCCH located in the subframe onwhich PDSCH is transmitted, when soft combining of EPDCCH is applied.

In other words, terminal 200 transmits A/N signals (response signals)for the downlink data on PUCCH associated with the ECCE located in asubframe to which the downlink data (PDSCH) is assigned among theplurality of subframes used for soft combining, the assignment of thedownlink data (PDSCH) being indicated by EPDCCH (DL assignment).Accordingly, when the ECCE number to be assigned varies depending on thesubframe, the ECCE associated with the PUCCH resource used fortransmission of A/N signals is not necessarily the smallest ECCE numberamong the ECCEs forming EPDCCH. Likewise, base station 100 (i.e.,reception section 107) receives A/N signals (response signals) for thedownlink data on PUCCH associated with the ECCE located in a subframe towhich the downlink data (PDSCH) is assigned among the plurality ofsubframes used for soft combining, the assignment of the downlink data(PDSCH) being indicated by EPDCCH (DL assignment).

For example, when PDSCH is located in the last subframe among theplurality of subframes to which soft combining of EPDCCH is applied,base station 100 and terminal 200 use the ECCE number of the EPDCCHlocated in the last subframe and thereby identify the PUCCH resource towhich the uplink A/N signals for the PDSCH are assigned. Morespecifically, PDSCH is located in subframe #1, which is the lastsubframe among subframes #0 and #1 to which soft combining of EPDCCH isapplied in FIG. 7. Accordingly, base station 100 and terminal 200identify the PUCCH resource associated with the ECCE number of theEPDCCH located in subframe #1, in subframe #5, which corresponds to thefourth subframe following subframe #1, as the PUCCH resource to whichthe uplink A/N signals for the PDSCH are assigned in FIG. 7.

Accordingly, even when an EPDCCH search space is shared between aterminal to which soft combining of EPDCCH is applied and a terminal towhich no soft combining of EPDCCH is applied, base station 100 assignsthe ECCE numbers used in the EPDCCH intended for these terminals in thesubframe to which the PDSCH intended for both of the terminals isassigned. Thus, in this subframe, the ECCE numbers are assignedconsidering a PUCCH resource collision between the terminals, so thatPUCCH resources are automatically (implicitly) assigned in a way thatavoids a PUCCH resource collision between the terminals.

(PUSCH Timing)

In LTE-Advanced, terminals transmit PUSCH after receiving UL grant. Thesubframe used for transmission of PUSCH is previously determined. Morespecifically, the fourth subframe following the subframe to which ULgrant is assigned is configured as the subframe on which PUSCH istransmitted in the FDD system, while the subframe on which PUSCH istransmitted is defined according to each TDD UL-DL configuration in theTDD system. In addition, when the number of UL subframes is greater thanthe number of DL subframes in a single frame, PUSCH on a plurality of ULsubframes may be specified in a single DL subframe. However, in thiscase as well, the subframe on which PUSCH is transmitted is alwaysconfigured to be the fourth subframe following the subframe to which ULgrant is assigned or a subframe after the fourth subframe.

Moreover, after detection of UL grant, terminals identify that the PRBpair specified by the UL grant is assigned to PUSCH and determine thesize and transmission method of data (PUSCH). Accordingly, unless atleast a certain interval after the last subframe (i.e., detection of ULgrant) among the subframes to which soft combining is applied isprovided (four subframes or more in LTE-Advanced), PUSCH transmissionprocessing cannot be prepared in terminals.

In this respect, the transmission timing of PUSCH specified by the ULgrant transmitted using EPDCCH to which soft combining is applied isidentified using, as the basis, the last subframe among the plurality ofsubframes on which the EPDCCH to be soft-combined is located inEmbodiment 1. Since the transmission timing of PUSCH (i.e., subframe onwhich PUSCH is transmitted and received) is identified using the lastsubframe used for soft combining, the interval from the detection timingof UL grant until preparation for PUSCH transmission can be the same asthe interval used when no soft combining of EPDCCH is applied.

In particular, in the TDD system, there is a subframe on which no ULgrant is transmitted among DL subframes in accordance with anassociation between transmission and reception timing of UL grant andtransmission and reception timing of PUSCH (i.e., UL grant-PUSCH timing)defined for each UL-DL configuration. In this respect, in the TDDsystem, the last subframe among the plurality of subframes used for softcombining is made the same as the transmission subframe for EPDCCHincluding UL grant (i.e., subframe in which EPDCCH including UL grant istransmitted).

FIG. 8 illustrates subframes in case of UL-DL configuration #1, forexample. As illustrated in FIG. 8, subframes #0, #4, #5, and #9 are DLsubframes, while subframes #1 and #6 are special subframes (i.e.,subframes that can be used for EPDCCH and PDSCH transmission), andsubframes #2, #3, #7, and #8 are UL subframes UL-DL configuration #1.Moreover, UL grant-PUSCH timing is previously defined as illustrated inFIG. 8, and the subframes on which UL grant can be located are subframes#1, #4, #6, and #9, and for the UL grant notified in each of thesubframes, PDSCH is assigned to UL subframes #7, #8, subframe #2 of thenext frame (not illustrated), and subframe #3 of the next frame.

Meanwhile, as illustrated in FIG. 8, when soft combining is applied,there is a case where UL grant is located in a subframe on which no ULgrant is transmitted. In this respect, in Embodiment 1, when softcombining of EPDCCH including UL grant is applied, the last subframeamong the subframes on which EPDCCH to be soft-combined is located isconfigured as a subframe capable of transmitting UL grant when no softcombining is applied.

In this configuration, soft combining can be utilized without changingPUSCH timing from the UL grant detection timing.

For example, only subframes #1, #4, #6, and #9 are configured as thelast subframe used for soft combining in FIG. 8. More specifically, softcombining of EPDCCH including UL grant is configured in each ofsubframes #0 and #1 and subframes #5 and #6 in FIG. 8. As illustrated inFIG. 8, EPDCCH including UL grant is located in subframes #0 and #5 onwhich no UL grant is located when no soft combining is applied. In thiscase as well, the transmission timing of PUSCH indicated by the UL grantnotified using the EPDCCH is identified on the basis of the lastsubframe among the subframes in which the EPDCCH is transmitted. In sum,when soft combining including UL grant is applied, the PUSCH timingspecified by the UL grant transmitted using EPDCCH to which softcombining is applied (i.e., first transmission subframe for PUSCH) isdefined using, as the basis, the last subframe on which EPDCCH to besoft combined is located. Accordingly, soft combining can be utilizedwithout any change in the relationship between the detection timing ofUL grant and the PUSCH timing compared to a case where no soft combiningis applied.

It should be noted that, when the subframe specified as a subframe towhich soft combining of EPDCCH is applied is common to DL assignment andUL grant, regarding UL grant, it is possible to employ a configurationin which soft combining is performed on condition that theabovementioned last subframe is configured as a subframe capable oftransmitting UL grant when no soft combining is applied, and no softcombining is performed when this condition is not satisfied.

Hereinabove, a description has been provided regarding the timing ofsignals (i.e., PDSCH, UL ACK/NACK, and PUSCH) when soft combining ofEPDCCH is applied.

Next, a description will be provided regarding switching between softcombining and non soft combining.

For example, in a subframe to which soft combining of EPDCCH is applied,the EPDCCH candidates in the same subframe may be divided into an EPDCCHcandidate for soft combining and an EPDCCH candidate for non softcombining. This configuration make it possible to flexibly switchbetween soft combining and non soft combining depending on instantchannel quality by selecting the EPDCCH candidate to be used in the samesubframe.

In the following example, the number of EPDCCH candidates for softcombining is referred to as “K1” and the number of EPDCCH candidates fornon soft combining is referred to as “K2.” FIG. 9A illustrates anexample of the relationship between the aggregation level (L), thenumber of PRB pairs, and the number of EPDCCH candidates inLTE-Advanced.

FIG. 9B illustrates an example in which the EPDCCH candidates in FIG. 9Aare divided into EPDCCH candidates for soft combining and EPDCCHcandidates for non soft combining when switching between soft combiningand non soft combining is employed.

Application of one of three methods 1 to 3 may be possible for utilizingEPDCCH for non soft combining, for example.

(Method 1)

In Method 1, EPDCCH for non soft combining can be located in anysubframe, but PDSCH notified by the EPDCCH is located in the subframecorresponding to the last subframe among the subframes to which softcombining is applied, and PUSCH notified by the EPDCCH is located in asubframe identified using the last subframe as the basis.

In Method 1, terminal 200 monitors (i.e., blind-decodes) K2 EPDCCHcandidates in subframes other than the last subframe and monitors K1+K2EPDCCH candidates in the last subframe.

According to Method 1, each of the PDSCH timing and PUSCH timing forsoft combining can be used when no soft combining is applied, whichmakes the scheduling simple. In particular, in UL HARQ, since the ULHARQ process number is determined depending on the subframe, it ispossible to switch between soft combining and non soft combining withoutchanging the UL HARQ process number.

(Method 2)

In Method 2, EPDCCH for non soft combining is located in a subframeother than the subframe corresponding to the last subframe among thesubframes to which soft combining is applied. More specifically, whenthe number of subframes to which soft combining is applied is two,EPDCCH for non soft combining is located in the first subframe.

In this case, terminal 200 monitors K2 EPDCCH candidates in the subframeother than the last subframe and monitors K1 EPDCCH candidates in thelast subframe.

According to Method 2, the number of EPDCCH candidates monitored byterminal 200 in each subframe can be averaged because the subframes thatbecome monitoring targets for EPDCCH candidates are distributed inaccordance with whether or not soft combining is applied.

In addition, a subframe on which EPDCCH for non soft combining istransmitted and a subframe on which PDSCH notified by this EPDCCH istransmitted may be configured as different subframes. This configurationcan separate an EPDCCH subframe and a data (PDSCH) subframe, thusallowing the power useable for EPDCCH transmission to be allocated todata transmission when the data transmission requires power.

(Method 3)

In method 3, EPDCCH for non soft combining can be located in anysubframe.

In method 3, terminal 200 monitors K2 EPDCCH candidates in a subframeother than the subframe corresponding to the last subframe among thesubframes to which soft combining is applied and monitors K1+K2 EPDCCHcandidates in the subframe corresponding to the last subframe.

In addition, PDSCH may be located in any subframe, and PUSCH is locatedin a subframe identified using the subframe on which EPDCCH is detected,as the basis.

According to method 3, PDSCH/PUSCH can be assigned more flexibly when nosoft combining is applied.

Hereinabove, a description has been given regarding switching betweensoft combining and non soft combining.

As described above, according to Embodiment 1, the transmission timingof each set of signals (resource allocation for each set of signals)when soft combining is applied can be appropriately configured.

It should be noted that, application of soft combining of PDSCH andPUSCH (sometimes, called “TTI bundling”) in combination with softcombining of EPDCCH described above may be possible. In this case, thefirst subframe of DL data (PDSCH) the assignment of which is indicatedusing DL assignment may be located in the last subframe among aplurality of subframes on which EPDCCH including the DL assignment istransmitted. In this configuration, the period for saving, in a buffer,the received signals that are received from the reception timing ofPDSCH to the completion of EPDCCH detection processing (i.e., signalsthat may be PDSCH) can be the same as the period used when no softcombining of EPDCCH is applied.

Embodiment 2

In Embodiment 2, a description will be provided regarding resourceallocation for EPDCCH (i.e., search space configuration) in a pluralityof subframes on which EPDCCH to be soft combined is located.

The base station and terminal according to Embodiment 2 include the samebasic configurations as base station 100 and terminal 200 according toEmbodiment 1. Accordingly, the description will be provided withreference to FIGS. 5 and 6.

In Embodiment 2, a single EPDCCH set is configured in each of aplurality of subframes used for soft combining. More specifically, aplurality of EPDCCH sets respectively configured in a plurality ofsubframes are connected to each other for soft combining of EPDCCH.

It should be noted that, the number of PRB pairs and a PRB pair number(frequency resource, i.e., PRB pair position) are configured for eachEPDCCH set. In addition, the number of PRB pairs determines N_(ECCE),which is the number of ECCEs in an EPDCCH set, and the ECCEs of ECCE #0to ECCE #N_(EccE)−1 are located.

FIG. 10 illustrates an example in which soft combining of EPDCCH isperformed using two subframes. It should be noted that, the bit sequenceof EPDCCH to be transmitted is previously configured as one that isequivalent to at least aggregation level 2 (at least AL2). In FIG. 10,the aggregation levels of EPDCCH #0 and EPDCCH #1 are AL2, and theaggregation level of EPDCCH #2 is AL4.

In Embodiment 2, each EPDCCH is divided into two EPDCCHs, and the twoEPDCCHs are respectively located on an ECCE of EPDCCH set 0 (EPDCCH setcorresponding to subframe #0) and an ECCE of EPDCCH set 1 (EPDCCH setcorresponding to subframe #1). In other words, each EPDCCH is divided inunits of ECCEs.

For example, in FIG. 10, EPDCCH #0 is divided into EPDCCH #0 aand EPDCCH#0 b, and EPDCCH #0 a and EPDCCH #0 b are respectively located on EPDCCHcandidates of AL1 (each candidate corresponding to one ECCE) of EPDCCHset 0 and EPDCCH set 1. Likewise, EPDCCH #1 is divided into EPDCCH #1 aand EPDCCH #1 b, and EPDCCH #1 a and EPDCCH #1 b are respectivelylocated on EPDCCH candidates of AL1 (each candidate corresponding to oneECCE) of EPDCCH set 0 and EPDCCH set 1. Likewise, EPDCCH #2 is dividedinto EPDCCH #2 a and EPDCCH #2 b, and EPDCCH #2 a and EPDCCH #2 b arerespectively located on EPDCCH candidates of AL2 (each candidatecorresponding to two ECCEs) of EPDCCH set 0 and EPDCCH set 1.

To put it differently, base station 100 (i.e., configuration section102) configures an EPDCCH set in each of a plurality of subframes usedfor soft combining. In addition, base station 100 (i.e., signalassignment section 105) divides EPDCCH (control information) into thesame number of EPDCCHs in units of ECCEs as the number of the pluralityof subframes and assigns each of the divided EPDCCHs to any of the ECCEsforming the EPDCCH set configured in one of the plurality of subframes.

In this case, the EPDCCH candidate for each terminal 200 variesdepending on the subframe number. Accordingly, as illustrated in FIG.10, the divided EPDCCHs are located on different EPDCCH candidates insubframes #0 and #1, respectively. In LTE-Advanced, studies have beencarried on two equations 1 and 2 below as equations for determiningEPDCCH candidates for each terminal 200.

$\begin{matrix}\left( {{Equation}\mspace{14mu} 1} \right) & \; \\{{L\left\{ {\left( {Y_{p,k} + m^{\prime}} \right){mod}\left\lfloor {N_{{ECCE},p,k}/L} \right\rfloor} \right\}} + i} & \lbrack 1\rbrack \\\left( {{Equation}\mspace{14mu} 2} \right) & \; \\{{L\left\{ {\left( {Y_{p,k} + \left\lfloor \frac{m^{\prime} \cdot N_{{ECCE},p,k}}{L \cdot M_{p}^{(L)}} \right\rfloor} \right){mod}\; \left\lfloor {N_{{ECCE},p,k}/L} \right\rfloor} \right\}} + i} & \lbrack 2\rbrack\end{matrix}$

In equations 1 and 2, L represents aggregation level (AL), Y_(p, k)represents UE ID (i.e., terminal ID), k represents subframe number, and_(p) represents search space set number. In addition, i takes on thevalue of 0, 1, . . . , L−1.

Moreover, m′ represents the parameter used when cross-carrier schedulingis configured and expressed by the next equation.

(Equation 3)

m′=m+M _(p) ^((L)) ·n _(CI)   [3]

M_(p) ^((L)) represents the number of EPDCCH candidates to be monitoredat aggregation level (L) and n_(CI) represents the parameter used inconfiguring cross-carrier scheduling (i.e., carrier indicator fieldvalue). In equation 3, m′=m when no cross-carrier scheduling isconfigured.

Moreover, m is expressed by the next equation.

(Equation 4)

m=0,1, . . . M _(p) ^((L))−1   [4]

More specifically, m represents the EPDCCH candidate number for eachaggregation level (L).

In Embodiment 2, each of the divided EPDCCHs is located on an EPDCCHcandidate represented by m (the same number between the subframes) ineach of the subframes to which soft combining is applied.

In this manner, EPDCCH candidate numbers to be used can be sharedbetween subframes. More specifically, in the subframes to which softcombining is applied (two subframes in this embodiment), the number ofcombinations of EPDCCH candidates that is equal to M_(p) ^((L))*M_(p)^((L)) patterns can be limited to M_(p) ^((L)) patterns. Even when anEPDCCH candidate of the same number m is used in subframes, the EPDCCHcandidate (ECCE) is different for each subframe. More specifically, evenwith the EPDCCH candidate of the same number m, the frequency resourceallocated to each subframe is different, so that frequency diversityeffect can be obtained. In addition, when the number of REs to beactually allocated varies for each ECCE number, the number of REs can beaveraged.

Next, a description will be provided regarding methods 1 and 2 forconfiguring an EPDCCH search space in subframes to which soft combiningis applied. It should be noted that, a case where soft combining isapplied over two subframes will be described as an example. However, thenumber of subframes used for soft combining is not limited to two andcan be three or more.

(Method 1: When EPDCCH Sets Configured in Two Subframes are the Same)

FIG. 11A illustrates an EPDCCH set configured for non soft combining andFIG. 11B illustrates EPDCCH sets configured for soft combining.

As illustrated in FIG. 11B, EPDCCH sets 0 and 1 respectively configuredin the two subframes to which soft combining is applied (first andsecond subframes) are assumed to be the same.

Accordingly, as illustrated in FIG. 11B, the EPDCCH sets respectivelylocated in the subframes include the same number of PRB pairs (four) andthe same PRB numbers (the same PRB pair arrangement positions). However,EREGs corresponding to EPDCCH candidates forming each EPDCCH set aredifferent in each of the subframes.

In this manner, EPDCCH candidates at each aggregation level (AL) areequal to each other between EPDCCH sets (i.e., between subframes towhich the same EPDCCH is assigned). Accordingly, all the EPDCCHcandidates can be used as search spaces for soft combining of EPDCCH.

In addition, since EPDCCH is located on the same PRB pairs in aplurality of subframes, precoding for demodulation reference signals(DMRS), which are the reference signals used for EPDCCH, can be sharedbetween the subframes. Accordingly, when the moving speed of terminal200 is slow, for example, an assumption can be made that channelfluctuation is small between contiguous subframes, so that terminal 200can combine the reference signals of a plurality of subframes to improvethe channel estimation accuracy.

In addition, LTE-Advanced allows each terminal to be configured with twoEPDCCH sets. Thus, it is possible to dynamically switch between softcombining and non soft combining by configuring one EPDCCH set for softcombining and the other EPDCCH for non soft combining.

(Method 2: When EPDCCH Sets Configured in Two Subframes are Different)

FIG. 12A illustrates EPDCCH sets for non soft combining, and FIG. 12Billustrates EPDCCH sets configured for soft combining.

As illustrated in FIG. 12B, EPDCCH sets 0 and 1 respectively configuredin the two subframes to which soft combining is applied (first andsecond subframes) are different.

In the subframes to which soft combining is applied, a single EPDCCH setis located in each of the subframes as illustrated in FIG. 12B, whiletwo EPDCCH sets are located in the subframe to which no soft combiningis applied as illustrated in FIG. 12A.

As illustrated in FIGS. 12A and 12B, the number of PRB pairs, the PRBnumbers (PRB pair arrangement positions), and the assignment method(distributed assignment or localized assignment) can be configured ineach of the EPDCCH sets respectively configured in the plurality ofsubframes used for soft combining. More specifically, soft combining canbe performed using EPDCCH sets that are different in design in Method 2.

For example, in FIG. 12B, among the two subframes to which softcombining of EPDCCH is applied, the number of PRB pairs of the EPDCCHset configured in the first subframe is four (N=4) and the number of PRBpairs of the EPDCCH set configured in the second subframe is two (N=2).As described, since the number of PRB pairs is different between thesubframes (between the EPDCCH sets), the number of EPDCCH candidates foreach aggregation level is also different. For example, as illustrated inFIG. 13, the numbers of EPDCCH candidates when the number of PRB pairsN=2 are 4, 2, 1, 1, and 0 for the ALs (L=1, 2, 4, 8, and 16),respectively, while the numbers of EPDCCH candidates when the number ofPRB pairs N=4 are 2, 3, 2, 1, and 1 for the ALs (L=1, 2, 4, 8, and 16),respectively.

In FIG. 13, with reference to AL1 (L=1, but L=2 when soft combining isapplied), the number of EPDCCH candidates when the number of PRB pairs=2is four (i.e., EPDCCH candidate numbers m=0, 1, 2, and 3), and thenumber of EPDCCH candidates when the number of PRB pairs 32 4 is two(i.e., EPDCCH candidate numbers m=0 and 1). In this case, base station100 and terminal 200 use only two EPDCCH candidates (m=0 and 1) commonto the two EPDCCH sets as the EPDCCH candidates for soft combining anduse the remaining EPDCCH candidates (i.e., two EPDCCH candidates m=2 and3 when the number of PRB pairs N=2) as the EPDCCH candidates for nonsoft combining. The same applies to the other ALs.

To put it differently, since the EPDCCH candidates for each AL aredifferent between EPDCCH sets, the EPDCCH candidates of the EPDCCH setsmaller in number are used as the search spaces for soft combining inMethod 2. In this case, the remaining EPDCCH candidates of the EPDCCHset larger in number can be used as the search spaces for non softcombining.

In addition, according to Method 2, the region used for EPDCCH can bechanged for each subframe. For example, when PDSCH is located in thelast subframe (e.g., second subframe in FIG. 12B) among the subframesused for soft combining, the EPDCCH region located in the last subframeis reduced in size compared with the other subframe (e.g., firstsubframe in FIG. 12B), which makes it possible to ensure the PDSCHregion.

Methods 1 and 2 for configuring search spaces have been described above.

As described above, according to Embodiment 2, the resource allocationfor locating EPDCCH when soft combining is applied can be appropriatelyconfigured.

It should be noted that, the number of EPDCCH candidates for each ALvaries depending on conditions such as a DCI format, bandwidth, subframetype and/or the number of subcarriers in EPDCCH of LTE-Advanced. Morespecifically, the abovementioned conditions are classified into Cases 1,2, and 3 in LTE-Advanced. Case 1 supports AL2 (L=2) or above, whileCases 2 and 3 support AL1 (L=1) or above. For this reason, althoughEmbodiment 2 has been described with the case assuming EPDCCH at AL2 orabove, EPDCCH at AL1 can be treated as EPDCCH at AL2 or above byapplication of soft combining. More specifically, in Embodiment 2, it ispossible to apply, to all DCI formats, not only Case 1 in which thenumber of EPDCCH candidates at AL2 or above is prepared, but also Cases2 or 3 in which the number of EPDCCH candidates at AL1 or above isprepared. In this manner, the AL can be prevented from rising too highin case of soft combining.

Embodiment 3

In Embodiment 2, a description has been given regarding the case wheresoft combining is performed while a plurality of EPDCCH setsrespectively configured in a plurality of subframes to which softcombining is applied are connected to each other. On the other hand, inEmbodiment 3, a description will be provided regarding a case where PRBpairs of a single EPDCCH set are distributed into a plurality ofsubframes to which soft combining is applied.

The base station and terminal according to Embodiment 3 include the samebasic configuration as base station 100 and terminal 200 according toEmbodiment 1. Accordingly, the description will be provided withreference to FIGS. 5 and 6.

More specifically, base station 100 (i.e., configuration section 102)configures a single EPDCCH set entirely for the plurality of subframesused for soft combining. However, the PRB pairs corresponding to theECCEs forming the single EPDCCH set are distributedly located in theplurality of subframes used for soft combining.

For example, when the number of PRB pairs of the EPDCCH set is N whilethe number of subframes used for soft combining is M, the number of PRBpairs obtained by dividing N by M (N/M) is located per subframe.

FIG. 14 illustrates an example in which soft combining of EPDCCH isperformed using two subframes (M=2). In FIG. 14, the number of PRB pairsof the EPDCCH set is set equal to four (N=4). Accordingly, two PRB pairs(=N/M) are located per subframe in FIG. 14. In FIG. 14, the aggregationlevels of EPDCCHs #0 and #1 are AL1, and the aggregation level of EPDCCH#2 is AL2. Moreover, each EPDCCH is located according to the assignmentmethod of ECCEs in EPDCCH set 0.

In FIG. 14, EPDCCH #0 is located on ECCE #0, while EPDCCH #1 is locatedon ECCE #1, and EPDCCH #2 is located on ECCEs #2 and #3. Each ECCE islocated on four PRB pairs of EPDCCH set 0 (e.g., PRB indices #0, #1, #2,and #3). However, PRB indices #0 and #2 are located in subframe #0, andPRB indices #1 and #3 are located in subframe #1 in FIG. 14. Morespecifically, single EPDCCH set 0 is located in a divided manner on aplurality of subframes to which soft combining is applied.

Accordingly, soft combining can be applied even when AL1 is used inEmbodiment 3. In addition, since the amount of resource for the EPDCCHregion per subframe used for soft combining can be reduced, the resourcenot used for EPDCCH can be used for PDSCH.

(Variation when N=8)FIG. 15 illustrates an example of a correspondencebetween ECCEs and PRB pairs when the number of PRB pairs of a searchspace set is eight (N=8), and the number of EREGs per ECCE is four. InFIG. 15, the PRB pairs on which ECCE is located vary depending on theECCE. More specifically, an even number (index) ECCE is located on evennumber PRB pairs, and an odd number ECCE is located on odd number PRBpairs.

A description will be provided regarding variations 1 and 2 of dividingan EPDCCH set (PRB pairs) into a plurality of subframes (i.e., twosubframes herein) used for soft combining in this case.

(Variation 1)

In Variation 1, in case of soft combining, subframes are separated intoa subframe on which even number PRB pairs are located and a subframe onwhich odd number PRB pairs are located. For example, when soft combiningis performed using two subframes, even number PRB pairs are located inthe first subframe and odd number PRB pairs are located in the secondsubframe.

Accordingly, EPDCCH at AL1 formed of single ECCE is located in one ofthe first and second subframes. To put it differently, no soft combiningis applied to EPDCCH at AL1 Thus, it is possible to switch between softcombining and non soft combining by selecting a certain AL.

As described above, soft combining can be applied using EPDCCH at AL2 orabove in Variation 1. In this respect, Case 1 prepared from the numberof EPDCCH candidates at AL2 (see, NPL 1) can be applied to all DCIformats in LTE-Advanced. Accordingly, soft combining can be applied toall EPDCCH candidates.

(Variation 2)

In Variation 2, in case of soft combining, a set of PRB pairs includingan even number PRB pair and an odd number PRB pair is located in asingle subframe. For example, when soft combining is performed using twosubframes, a set of PRB pairs #0, #1, #4 and #5 is located in the firstsubframe, and a set of PRB pairs #2, #3, #6 and #7 is located in thesecond subframe in FIG. 15.

In this manner, even when EPDCCH at AL1 formed of single ECCE is used,EPDCCH is located in each of the first and second subframes.Accordingly, soft combining can be applied to EPDCCH at AL1 Thevariations of dividing an EPDCCH set (PRB pairs) for a plurality ofsubframes has been described.

As described above, according to Embodiment 3, resource allocation forlocating EPDCCH when soft combining is applied can be appropriatelyconfigured as in Embodiment 2.

The embodiments of the claimed invention have been described.

Other Embodiments

(1) When soft combining is applied, the number of EPDCCH candidates foreach AL may be changed. For example, FIG. 16A illustrates the number ofEPDCCH candidates for each AL before any change is made, and FIG. 16Billustrates the number of EPDCCH candidates for each AL after somechanges are made (for soft combining). In FIG. 16B, the number of EPDCCHcandidates for the high AL (L=8) is increased while the number of EPDCCHcandidates for the low AL (L=2) is decreased. The increase in the numberof EPDCCH candidates for a high AL particularly increases the softcombining effects.

(2) Although the description has been given regarding the case wherecontiguous subframes are used as the subframes used soft combining asillustrated in FIGS. 7 and 8, for example, the subframes used for softcombining do not have to be necessarily contiguous, and non-contiguoussubframes may be used.

(3) The precoding of DMRS in each subframe may be assumed to be the samedepending on conditions when soft combining of EPDCCH is performed inEmbodiments 2 and 3.

Examples of the conditions include a case where the PRB pairs on whichEPDCCH to be soft combined are located are identical between thesubframes. For example, in Embodiment 2 (Method 1), since the sameEPDCCH set is used in a plurality of subframes used for soft combining,it is possible to assume that the precoding of DMRS is the same in thesubframes.

Another example of the conditions is a case where the PRB pairs on whichEPDCCH is located are arranged within a constant range in each subframeto which soft combining is applied, for example. The term “within aconstant range” as used herein refers to adjacent PRB pair indices, forexample.

Still another example of the conditions is a case where the PRB pairs onwhich EPDCCH is located are arranged within a PRB bundling range in eachsubframe to which soft combining is applied. The term “PRB bundlingrange” as used herein refers to a value that is determined according tothe bandwidth and includes patterns of one, two, and three PRB pairs.

In Embodiment 3, the PRB pairs (positions) are always different betweenthe plurality of subframes, and it is thus difficult to set the sameprecoding of DMRS in the subframes. In this respect, when Embodiment 3is employed, the same PRB pairs may be used between the subframes usedfor soft combining. For example, in two subframes used for softcombining, the position of the PRB pair used in the second subframe maybe shifted in such a way that the PRB pair used in the second subframeis identical with the PRB pair used in the first subframe.

(4) In the embodiments described above, the cases where soft combiningis performed over a plurality of subframes (i.e., in the time domain)have been described. However, the embodiments may be applied in thefrequency domain (e.g., carrier aggregation). In this case, EPDCCH maybe located over a plurality of component carriers (CCs) instead oflocating EPDCCH on a plurality of subframes in the embodiments describedabove. In Embodiment 1, the PUCCH resource is implicitly indicated bythe ECCE (index) of EPDCCH located in the last subframe among aplurality of subframes, for example. Meanwhile, the PUCCH resource maybe implicitly indicated by the ECCE (index) of EPDCCH located on thePCell among a plurality of component carriers in case of carrieraggregation.

(5) Soft combining of EPDCCH in Embodiment 2 may be applied to twoEPDCCH sets in the same subframe. In this configuration, the maximum ALin a single subframe can be made larger, and the reception quality ofEPDCCH in a subframe having poor reception quality can be improved.

(6) The embodiments have been described by examples of hardwareimplementations, but the claimed invention can be also implemented bysoftware in conjunction with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor, whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

A base station according to this disclosure includes: a configurationsection that configures an Enhanced Physical Downlink Control Channel(EPDCCH) set in a plurality of subframes, the EPDCCH set being formed ofEnhanced Control Channel Elements (ECCEs) to which control informationtransmitted over the plurality of subframes is assigned; and anassignment section that assigns the control information to any of theECCEs on a Physical Resource Block (PRB) pair in each of the pluralityof subframes.

In the base station according to this disclosure, the configurationsection configures the EPDCCH sets respectively in the plurality ofsubframes, and the assignment section divides the control informationinto the same number of pieces of control information as the number ofthe plurality of subframes in units of the ECCEs and assigns each of thedivided pieces of control information to any of the ECCEs forming theEPDCCH sets configured respectively in the plurality of subframes.

In the base station according to this disclosure, the EPDCCH setsconfigured respectively in the plurality of subframes are the same.

In the base station according to this disclosure, the EPDCCH setsconfigured respectively in the plurality of subframes are different.

In the base station according to this disclosure, configuration sectionconfigures the single EPDCCH set entirely for the plurality ofsubframes, and PRB pairs corresponding to the ECCEs forming the singleEPDCCH set are distributedly located in the plurality of subframes.

In the base station according to this disclosure, the assignment sectionassigns downlink data to the last subframe among the plurality ofsubframes, the assignment of the downlink data being indicated by thecontrol information.

The base station according to this disclosure further includes areception section that receives response signals for downlink data on aPhysical Uplink Control Channel (PUCCH) associated with the ECCE locatedin a subframe to which the downlink data is assigned among the pluralityof subframes, the assignment of the downlink data being indicated by thecontrol information.

In the base station according to this disclosure, a transmissionsubframe for the control information indicating assignment of uplinkdata is associated with a reception subframe for the uplink data, andthe last subframe among the plurality of subframes is the same as thetransmission subframe.

A terminal according to this disclosure includes: a configurationsection that identifies Enhanced Control Channel Elements (ECCEs) towhich control information transmitted over a plurality of subframes isassigned, the ECCEs forming an Enhanced Physical Downlink ControlChannel (EPDCCH) set configured in the plurality of subframes; and areception section that receives the control information assigned to anyof the ECCEs on a Physical Resource Block (PRB) pair in each of theplurality of subframes.

A transmission method according to this disclosure includes: configuringan Enhanced Physical Downlink Control Channel (EPDCCH) set in aplurality of subframes, the EPDCCH set being formed of Enhanced ControlChannel Elements (ECCEs) to which control information transmitted overthe plurality of subframes is assigned; and transmitting the controlinformation assigned to any of the ECCEs on a Physical Resource Block(PRB) pair in each of the plurality of subframes.

A reception method according to this disclosure includes: identifyingEnhanced Control Channel Elements (ECCEs) to which control informationtransmitted over a plurality of subframes is assigned, the ECCEs formingan Enhanced Physical Downlink Control Channel (EPDCCH) set configured inthe plurality of subframes; and receiving the control informationassigned to any of the ECCEs on a Physical Resource Block (PRB) pair ineach of the plurality of subframes.

INDUSTRIAL APPLICABILITY

The claimed invention is useful in mobile communication systems.

REFERENCE SIGNS LIST

-   100 Base station-   200 Terminal-   101 Assignment information generating section-   102, 205 Configuration section-   103, 207, Error correction coding section-   104, 208 Modulation section-   105, 209 Signal assignment section-   106, 210 Transmission section-   107, 201 Reception section-   108, 203 Demodulation section-   109, 204 Error correction decoding section-   202 Signal demultiplexing section-   206 Control signal receiving section

1. A base station comprising: a configuration section that configures anEnhanced Physical Downlink Control Channel (EPDCCH) set in a pluralityof subframes, the EPDCCH set being formed of Enhanced Control ChannelElements (ECCEs) to which control information transmitted over theplurality of subframes is assigned; and an assignment section thatassigns the control information to any of the ECCEs on a PhysicalResource Block (PRB) pair in each of the plurality of subframes.
 2. Thebase station according to claim 1, wherein the configuration sectionconfigures the EPDCCH sets respectively in the plurality of subframes,and the assignment section divides the control information into the samenumber of pieces of control information as the number of the pluralityof subframes in units of the ECCEs and assigns each of the dividedpieces of control information to any of the ECCEs forming the EPDCCHsets configured respectively in the plurality of subframes.
 3. The basestation according to claim 2, wherein the EPDCCH sets configuredrespectively in the plurality of subframes are the same.
 4. The basestation according to claim 2, wherein the EPDCCH sets configuredrespectively in the plurality of subframes are different.
 5. The basestation according to claim 1, wherein the configuration sectionconfigures the single EPDCCH set entirely for the plurality ofsubframes, and PRB pairs corresponding to the ECCEs forming the singleEPDCCH set are distributedly located in the plurality of subframes. 6.The base station according to claim 1, wherein the assignment sectionassigns downlink data to the last subframe among the plurality ofsubframes, the assignment of the downlink data being indicated by thecontrol information.
 7. The base station according to claim 1, furthercomprising a reception section that receives response signals fordownlink data on a Physical Uplink Control Channel (PUCCH) associatedwith the ECCE located in a subframe to which the downlink data isassigned among the plurality of subframes, the assignment of thedownlink data being indicated by the control information.
 8. The basestation according to claim 1, wherein a transmission subframe for thecontrol information indicating assignment of uplink data is associatedwith a reception subframe for the uplink data, and the last subframeamong the plurality of subframes is the same as the transmission subframe.
 9. A terminal comprising: a configuration section that identifiesEnhanced Control Channel Elements (ECCEs) to which control informationtransmitted over a plurality of subframes is assigned, the ECCEs formingan Enhanced Physical Downlink Control Channel (EPDCCH) set configured inthe plurality of subframes; and a reception section that receives thecontrol information assigned to any of the ECCEs on a Physical ResourceBlock (PRB) pair in each of the plurality of subframes.
 10. Atransmission method comprising: configuring an Enhanced PhysicalDownlink Control Channel (EPDCCH) set in a plurality of subframes, theEPDCCH set being formed of Enhanced Control Channel Elements (ECCEs) towhich control information transmitted over the plurality of subframes isassigned; and transmitting the control information assigned to any ofthe ECCEs on a Physical Resource Block (PRB) pair in each of theplurality of subframes.
 11. A reception method comprising: identifyingEnhanced Control Channel Elements (ECCEs) to which control informationtransmitted over a plurality of subframes is assigned, the ECCEs formingan Enhanced Physical Downlink Control Channel (EPDCCH) set configured inthe plurality of subframes; and receiving the control informationassigned to any of the ECCEs on a Physical Resource Block (PRB) pair ineach of the plurality of subframes.